This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Male factor infertility is a significant concern throughout the world. The majority of the male infertility cases are idiopathic. In the male, primordial germ cells (PGCs) migrate, proliferate, and colonize the genital ridges to ultimately form testicular cords, where they establish contacts with the Sertoli cells. Key factors that regulate primordial germ cell migration and proliferation are not completely understood. The long-term goal of this project is to delineate the mechanisms of germ cell interactions with Sertoli cells in the testis. A mechanistic understanding of how germ cells develop and function is relevant to clinical conditions of male infertility that manifest as Sertoli cell-only syndrome for which there is currently no treatment. To begin to explore the developmental biology of the male germ cells and to understand the pathobiology of the human Sertoli cell-only syndrome, we have characterized atrichosis, the naturally occurring homozygous recessive mouse mutant. The atrichosis mutant testis histology closely resembles that of Sertoli cell-only syndrome patients and demonstrates tubules lined with only Sertoli cells and contains no germ cells. We will test the central hypothesis that a cell autonomous defect leads to complete absence of germ cells in the atrichosis mutant testis. These studies will identify the gene(s) responsible for the absence of germ cells in the atrichosis mutant mouse and provide a starting point for further loss-of-function and gain-of-function genetic approaches to understand germ cell migration and function. Finally, this work will establish atrichosis mutant as a genetically trackable new mouse model for human male infertility conditions associated with Sertoli cell-only tubules and germ cell aplasia, thus impacting clinical protocols of male fertility restoration.